Since a cured product obtained from an epoxy resin has excellent heat resistance and humidity resistance, besides applications for an adhesive, a molding material, a coating material, a photoresist material, a color developer, and the like, an epoxy resin has been widely used in electric and electronic fields including a semiconductor sealing material and a printed circuit-board insulating material.
In the printed circuit board field among the various applications described above, in concomitance with the trend toward reduction in size and improvement in performance of electronic apparatuses, the trend toward an increase in density by reduction in wiring pitch of semiconductor devices has been significant, and as a semiconductor mounting method corresponding to this trend, a flip chip connection method has been widely used in which a semiconductor device and a board are connected to each other with solder balls provided therebetween. Since this flip flop connection method is a semiconductor mounting method using a so-called reflow method in which after solder balls are disposed between a circuit board and a semiconductor device, melt welding is performed by heating the entire system, the circuit board itself is exposed to a high temperature environment during solder reflow, and a large stress is generated in the solder balls connecting the circuit board and the semiconductor device due to thermal contraction of the circuit board, so that a connection defect of wires may occur in some cases. Hence, as an insulating material used for printed circuit boards, a material having a low coefficient of thermal expansion has been demanded.
In addition, in recent years, because of regulations on environment issues and the like, a high melting point solder containing no lead has become a mainstream, and hence, the reflow temperature is increased. As a result, the change in heat resistance of an insulating material occurs during reflow, and a connection defect caused by warpage of a printed circuit board has become a serious problem. That is, a material having a small change in properties during reflow has been demanded.
In order to respond to the demand as described above, for example, a thermosetting resin composition containing as a main component, a naphthol novolac type epoxy resin obtained by a reaction between naphthol, formaldehyde, and epichlorohydrin has been proposed as a solution to achieve a technical subject such as a low temperature expansion property (see the following Patent Literature 1).
However, because of a high rigidity of the skeleton of the above naphthol novolac type epoxy resin as compared to that of a general phenol novolac type epoxy resin, although an effect of improving the coefficient of thermal expansion of a cured product to be obtained is observed, this improvement is not sufficient to satisfy the level which has been required in recent years. In addition, since the heat resistance of the cured product is remarkably changed due to a thermal history applied thereto, the change in heat resistance after reflow is large in the printed circuit board application, and hence, the above connection defect of a printed circuit board is liable to occur.